Hi all! In this post, we shall discuss the Children of Destiny, Ninian and Nils! First of all, their background. 
(Info. from Fire Emblem Wiki)

Ninian is a quiet, sweet, and polite dancer and the older sister of Nils, a teenage bard.

Ninian and Nils' lineage was half-human, but also half-dragon, their father speculated to be, ironically, the antagonist Nergal, and their mother an ice dragon knownas Aenir, kidnapped during the Scouring. Nergal decide to search for her, but left explicit instructions to the infant Ninian and Nils to return to pass through the Dragon's Gate after a period of time, should he not return. Ninian and Nils waited, but Nergal never returned, and they passed through the Dragon's Gate in their dragon forms, losing most of their memories, excluding some including their missing mother, which Ninian kept as a silver ring known as Ninis' Grace as a memento. They eventually settled in Paradise, but longed for Elibe, their birthplace. Thus, when they received an oppurtunity to return through the Dragon's Gate and back to the human realm, they quickly cooperated and passed through the Gate, losing most of their quintessence and being forced to revert to their human forms.

Now, for their stats. Ninian and Nils are dubbed the best Dancer/ Bard in the Fire Emblem games. This is because they have an interesting background and have very good growth rates, with the exception of their Strength and Skill, like all other Dancers and Bards. They have great HP, Speed, Luck and Resistance and have moderately good Defense. As an addition, they can use certain special Dance Rings. Here are the special Dance Rings and what they do: